Process for producing cup-shaped thin-walled metal wares

ABSTRACT

There is provided a metal forming process and apparatus for the production of cup-shaped tubular wares. Said process and apparatus are particularly adapted to the production of thinwalled tubular cup shapes having internally tapered walls.

United States Patent Banks, Jr. [451 Aug. 22, 1972 PROCESS FOR PRODUCING CUP- 3,433,040 3/1969 Lenz ..72/1 18 SHAPED THIN-WALLED METAL 3,098,285 7/ 1963 I Kelzenberg et al. ..72/82 WARES 2,408,596 10/ 1946 Bednar et al. ..72/84 2,691,818 10/ l 954 Rockwell, Jr ..72/82 [72] invent g? F l? 5; lmgtm 2,699,596 1/1955 Aronson ..72/82 2,522,257 9/1950 Curtis.. ..72/70 [22] Filed: Sept. 17, 1969 3,406,554 10/1968 Frankenberg ..72/333 [21] AWL NOJ 858,681 3,556,032 l/l97l Fraze ..1 13/120 H Primary Examiner-Charles W. Lanham [52] US. Cl ..113/120 H, 72/69, 72/82 Assistant Examiner-Michael J. Keenan [51] Int. Cl ..B2ld 51/00, B21b 27/06 Att0meyWilliam N. Anastos [58] Field of Search ..72/69, 286, 82, 83, 84, 85;

113/120 H [57] ABSTRACT There is provided a metal formingprocess and ap- [56] References cued paratus for the production of cup-shaped tubular UNITED STATES PATENTS wares. Said process and apparatus are particularly adapted --to the production of thin-walled tubular cup 2,330,81 l [0/1943 Damer et al ..72/69 1 2,503,464 4/1950 Bannister ..72/85 shapes havmg 'memany tapered wal Powers ..72/69 8 Clains, 2 Drawing Figures PROCESS FOR PRODUCING CUP-SHAPED THIN- WALLED METAL WARES THE PRIOR ART The art of producing cup-shaped tubular wares from ductile metals has, heretofore, generally involved a metal forming process known as cup drawing. Said process begins with a circular blank of sheet metal which is placed upon a circular die means. A punch member, of appropriate diameter, is then forced axially into the center of the metal blank and die means, thereby drawing the overlapping portion of the metal blank into the restricted annular space formed between the die means and punch. A variant of the above process, known as step drawing, is often utilized in the production of thin-walled tubes. In step drawing, a circular die member has coaxially positioned therewith a plug mandrel, thereby defining an annular space between the circular die and mandrel. An oversized tube is then forced into said annular space.

While the above drawing processes are frequently acceptable, particularly from the standpoint of simplicity and smooth surface characteristics imparted to the products formed thereby, said processes nonetheless suffer from certain serious deficiencies. Firstly, un-

' less the draw" is relatively short and/or the metal to be formed exceptionally ductile, it is ordinarily necessary to repeat the aforementioned drawing steps several times utilizing progressively smaller dies, punches and plugs in order to provide overall deep draws, i.e., draws where the original thickness of the metal blank is tov be reducedby a factor of more than about four, commonly referred to as ironing. Accordingly, cup or step drawing to substantial depths often requires a plurality of drawing passes which, of course,.is very expensive. Secondly, many metals undergo work hardening or crystallization during each drawing step, often rendering the product of each such drawing step unsuitable for further drawing unless specially treated, as by annealing. For instance, such items as brass small arms cartridge cases are often formed by cup drawing in a succession of drawing steps interspersed with time consuming and expensive annealing or stress relieving steps.

In recent years the provision of hermetic metal/glass seals has become an increasingly important art. For instance, specialty light bulbs or piping in many chemical processes requires the provision of hermetic seals between glass and tubular metal structures. Such seals are often formed by forcing tubular molten glass over the wall of the tubular metal structure. Upon cooling and shrinking, the glass tube forms a hermetic seal with the metal tube. Further, it is known that when the wall of the tubular metal structure is both thin and tapered, a glass/metal seal of superior quality is often achieved. To reap the full rewards in the use of tapered wall tubular structures, however, it is further important that the metal surface contacting the glass be smooth and free of surface defects. All of the above discussion points to the need in the metal-forming art for a simple accurate process and apparatus for forming tapered wall tubular wares.

While swaging, and particularly rotary swaging, may at first appear to be an attractive method for producing tapered wall tubular wares, said process has been found to be useful only when the wall thickness of the resulting product is not particularly important because the swaging processes tend to thicken the swaged part of the tube. Thus, a 2-inch OD metal tube with a 0.100 inch wall thickness when tapered to a diameter of 1- inch OD by rotary swaging will normally be found to have a wall thickness of approximately 0.200 at the 1- inch OD section of the finished product.

Accordingly, in the past when tapered wall tubular shapes were desired, it was generally necessary to produce same by providing an excessively thick tube and thereafter tapering the walls thereof by machining, suchas by taper reaming. In addition to the fact that such machining was expensive and time consuming, such machining was also often found unsatisfactory because stringent tolerances for. concentricity, particu- I larly with respect to thin wall tubing, could not ordinarily be met by production machining methods. Furthermore, such machining often leaves tool marks which, as mentioned before with respect to surface defects, is a detrimental feature when the finished tubular ware is to be subsequently utilized as part of a hermetic glass/metal seal. Thus, such machined wares are often required to be even further treated by a bumishing or polishing step.

In accordance with the apparatus and process of .the instant invention, however, cup-shaped tubular metal wares (hereinafter referred to for convenience as tubular wares), and particularly tubular wares having thin and accurately tapered walls, are readily formed.

OBJECTS OF THE INVENTION It is a principal object of the present invention to provide a novel metal forming process for the production of tubular wares.

It is another object of the present invention to provide a novel metal forming process for the production of tubular wares having thin walls.

GENERAL DESCRIPTION OF THE INVENTION In accordance with the process of the present invention tubular wares having wall thicknesses of less than 0.005 inches and most preferably less than 0.001 inches are formed by positioning a cup workpiece over a mandrel and forcing the resulting mandrel/cup workpiece assembly axially into the nip provided between said mandrel and at least one roller means. The mandrel and/or roller means are rotated as the workpiece is forced into said nip.

THE DRAWINGS FIG. 1 is a schematic diagrammatic longitudinal section of suitable apparatus for performing the process of the invention wherein there is provided a mandrel, a

workpiece positioned thereon, and a roller holding means. v

- F 16.2 is a schematic diagrammatic longitudinal section of a typical product of the process of the present invention. I

DETAILED DESCRIPTION or THEINVENTION Referring to the drawings, the apparatus of the invention broadly comprises mandrel 3 and rollers 9 disposed substantially equiangularly and equidistantly about the axis of said mandrel 3. It is to be noted that,

in the present instance, only two of three rollers 9 are shown due to the section of the drawing. However, as will be obvious to those conversant with the machining arts, the use of three-rollers is indicated by the fact that rollers 9 of the depicted apparatus are spaced at 120 angles from one another. Said rollers 9 are sturdily and rotatably mounted in any appropriate static holders 11. Additionally, means are provided (not shown) to rotate mandrel 3 about its axis and to feed said mandrel 3 longitudinally and substantially coaxially through the zone defined by said rollers 9. In this context it is to be noted and understood that the longitudinal feed and rotation system provided is intended broadly to provide longitudinal and rotational motion of the mandrel relative to rollers 9. Accordingly, it is also suitable that mandrel 3 be statically mounted while holders ll be provided with means for rotating and feeding rollers 9 axially over said statically mounted mandrel. Other permutations and combinations of such means to accomplish the intended relative motions of the mandrel and roller means are also generally suitable and will be recognized by those skilled in the art.

- In a preferred embodiment of the invention,- however, static holders 1 1 each have associated therewith a heating means, such as cartridge heaters 15. When this preferred embodiment is employed, it will normally facilitate matters substantially if holders 11 are mounted statically while provision is made to rotate and feed mandrel 3.

The particular contour of rollers 9 employed in the apparatus is not normally critical. Thus, for instance, cylindrical, spherical or divergently tapered contours are often entirely suitable. However, depending largely upon such operating parameters as the specific metal to be formed, the extent of reduction of wall thickness of the metal to be accomplished, the temperature at which operations are to take place, the number of passes to be employed to attain the finished product, etc., I generally prefer that rollers 9 have longitudinally stepped contours. Specifically, rollers 9 bear steps 17 and 19 constituted by incrementally increasing roller diameters; The provision of such stepped roller contours can serve, practically speaking, as means for providing several forming operations with each pass of a workpiece therethrough. Accordingly, said stepped rollers 9 can often accomplish in one pass what would normally require three or more passeswhen essentially cylindrical rollers are employed. a

While choice of the materials of construction of the remainder of the apparatus will generally be obvious to those skilled in machine design, it is pointed out that'it ismuch preferred that the materials of construction of rollers 9 be chosen so as to provide'as hard and smooth a roller surface" as possible, bearing in mind of course the particular needs of the'metals and tubular wares to be formed therewith. Generally speaking, however,

materials such as cemented tungsten carbide, hardened or normalized tool steel, and nitrided or case hardened steels, i.e., materials which are, or can be treated to be, harder than about Rockwell C-60 'are generally much preferred as materials of construction for the roller means. Referring now to the operations of the aforedescribed apparatus with respect to a particular end product, cup workpiece Scomprising a crossrolled 0.020 inch molybdenum sheet which had been blanked, cup drawn and trimmed into a cup havingan ID. of about 0.490, a height of about one-half inch, side wall 6 thickness of about 0.020 inch and base wall 7 thickness of about 0.020 inch was positioned over tapered round mandrel 3 having a tip 8 diameter of 0.485 inch and a divergent taper beginning 0.5 inch from tip 8 and extending rearwardly from said tip 8 for a distance of 1.25 inches to a diameter of 0.497 inch. Said mandrel 3 was heated to and maintained at a temperature of about 400 F by means of thermostatically controlled cartridge heater l6 embedded therein. Next, said mandrel 3, bearing the cup workpiece 5 thereon was rotated at a speed of 500 r.p.m. and fed at a rate of 0.001'inch/revolution coaxially into the area defined by step-contoured cemented tungsten carbide rollers 9 having step diameters in increasing order of 1.00 inch, 1.02 inches and 1.04 inches, respectively. Prior to start-; up, said rollers were adjusted so as to provide a 0.0015 inch clearance between their respective i 1.04 inch diameter steps and the 0.497 inch diameter portion of tapered mandrel 3. Additionally, holders 11 were each continuously heated by means of cartridge heaters 15 so as to minimize heat flux into the rollers and sundry apparatus from the workpiece undergoing forming.

When the mandrel tip 8 had traversed through-the space defined by rollers 9 to a depth of about 1.2 inches, mandrel 3 was withdrawn and the formed tubular ware removed from the mandrel. Said ware was then trimmed to an overall length of thirty-one/thirtyseconds inch and inspected visually and dimensionally.

The surface of the finished cup product was found to be smooth and substantially free of burrs, tool marks or other surface defects and was further adjudged to have a finish of about 20 ms. Dimensionally, the ware was found to possess a uniform CD. of about 0.530 inch and a substantially linear internal taper having a thickness of 0.02 inch at the base of the vertical wall and tapering to a thickness of 0.0015 inch at the open mouth thereof. 7

Generally speaking, any metal, metal alloy or mix-. ture thereof having suitable ductility constitutes a suitable metallic material for forming by the process of the invention. While direct measurement of ductility may be had by resorting to analytical tests such as' the Vickers, Erichson or Olsen tests, a physical parameter generally more readily extracted from the literature 9 than data relating to any of the above-mentioned tests is percent elongation at yield. Said parameter also constitutes a good indication of ductility. Suffice it to say,

therefore, that any metal material having an ultimate mate percent elongation of at least about 20 percent.

As will be readily recognized by those skilled in the art, the physical and thermal history of a metal often determines its elongation properties and such properties may often be further altered or modified by suitable treatment of the metal, such as by annealing. Accordingly, the above elongation criteria are intended to be imposed upon the metal material subsequent to the forming thereof into cup workpiece 5. Further, when said workpiece 5 is to be formed at elevated temperatures, the percent elongation criteria are to be taken at the intended temperature of operations. Specific examples of normally suitable metal materials for forming by the process and apparatus of the invention are: wrought iron, hot or cold rolled iron, structural steels, SAE 1300 steel, SAE 4340 steel, SAE l 1 12 cold rolled steel, 18-18 stainless steel, aluminum, l7ST aluminum, annealed copper, brass, phosphor, bronze, Monel metal, molybdenum, zirconium, titanium, nickel, German silver, gold, platinum, rhodium, zinc, beryllium, cobalt, iridium, magnesium, palladium, tantalum, vanadium, and the like. The present invention is particularly useful, however, with molybdenum, copper, nickel alloys and particularly nickel-iron alloys, and tantalum which appear to lend themselves particularly well to the present process and which are very difiicult to handle by conventional processes.

In the practice of my invention it has been noted that when rolled sheet metals are utilized as starting materials, it is often desirable that said sheet metals be of the cross-rolled variety rather than those rolled in one direction. This is particularly important when certain metals are employed which are known to have significantly higher tensile strengths parallel to the direction of roll than at 90 thereto. For example, molybdenum, when utilized in the present invention in the form of a unidirectionally rolled sheet frequently fractures or produces uneven surfaces. When molybdenum has been cross-rolled, however, this problem either does not occur or occurs only to a lesser degree.

Cup workpiece 5 is generally described as a cup shaped ware having a side wall 6 of sufficient thickness to provide a volume of material sufficient to substantially completely fill the nip between mandrel 3 and roller means 9 for the entire length of the ultimately formed tubular product. Preferably, a slight excess of metal material will normally be provided.

Major practical purposes served by cup workpiece 5 are of course to provide (1) a sufiicient volume of metal material for forming, and (2) a convenient shape which, when emplaced on mandrel 3, is stable thereon until the actual forming operation of the invention is under way. Accordingly, it is only necessary that said cup workpiece have a wall 6 length sufficient to ensure said stability; however, it may also obviously be as long as desired. In this context, it is important to note that the process of the present invention does not normally result in significant reduction in the thickness of base wall 7 of cup workpiece 5. Accordingly, when determining the volume of material necessary to achieve the above-described complete fill between mandrel 3 and roller means 9, the volume of material to be employed in base wall 7 should normally be discounted. Base wall 7, however, serves the purpose of providing a thrust member against which mandrel 3 is forced during operations. Accordingly, the thickness of said base wall 7 should be chosen, bearing the strength of the metal material in mind, so as to be sufiicient to withstand the operational thrust loads imposed thereupon by said mandrel 3 without fracture, tearing or substantial distortion thereof. Further, the ID. of the workpiece cup is beneficially chosen so as to provide a press-/or slip-fit thereof over the mandrel.

The particular method utilized in forming workpiece 5 is normally non-critical provided that the finished product adheres to the above-described dimensional and physical criteria. Accordingly, said cup may be formed by standard cup drawing, swaging, powder metallurgical techniques and the like.

The feed rates and rotational speeds employed during the forming operation of the invention are also subject to wide variation. The choice of said feed rate and rotational speed will be dictated, to a large extent, by such parameters as the temperature of operations, the material to be formed, the thickness of the cup work piece, and particularly the relation of said thickness to the thickness of the intended end product tubular ware,

. the form of the rollers, etc. Generally, it can be said that the more ductile the metal of the cup workpiece and/or the 'less the reduction in thickness of the sidewall thereof contemplated, the faster can be the feed rate. Nevertheless, it is important that the feed of the mandrel into the rollers be accomplished smoothly and substantially continuously as opposed to a stepwise, discontinuous fashion. Such can be provided by the use ofa jack screw feed mechanism or the like. The final choice of feed rate and rotational speeds to be employed in any given case can best be determined in practice.

With respect to temperature of operation, it will be recognized that many metal materials have definite optimum forming temperature ranges. For instance, we have found that cross-rolled molybdenum can generally be best formed in the process of the invention at temperatures of between about 300 F and about 500 F and most preferably between 375 F and about 425? F. However, the optimum temperature ranges to be employed for other metal materials will obviously vary. Accordingly, suffice it to say that elevated operational temperatures will often be preferred in the practice of the invention.

The particular method by which the workpiece and forming apparatus are heated is not normally critical. For example, hot gases may be flowed through the operational environment or flames may be impinged on the rollers, workpiece and mandrel. The employment of electric cartridge heaters as previously described, however, represents a greatly preferred expedient for performing the heating function due, in large measure, to the simplicity of the apparatus required and the excellent temperature control normally achievable therewith.

While a single roller means 9 may be employed in the practice of the invention, it will be realized that the biasing forces brought to bear against the mandrel by a single roller during operations will normally be rather great. Accordingly, it is suggested that when the use of a single roller means 9 is contemplated, its use be restricted to those operations in which mandrel 3 has a substantial diameter and the amount of thickness reduction to be accomplished on sidewall 6 of cup workpiece 5 is small, or conversely, that means be provided to support mandrel 3 against the biasing forces encountered during operations. Much preferred, however, is an arrangement of a plurality of roller means 9 in which the vector sum of the aforesaid biasing forces encountered during operations is substantially zero. In

, therefore, the major operational forces encountered by the mandrel during operations will be compressive forces due to the pressure exerted thereon through the workpiece by the rollers and torsional forces encountered as a result'of the rotation of the rollers relative to the mandrel. The cylindrical shape of the mandrel, however, ideally befits this element to readily withstand such compressive and torsional forces.

Obviously, many-changes and additions can be made to the above-description of theapparatus and process of the invention. For instance, while not specifically mentioned above,.various lubricants can be employed during operations.

Also, the forming of a tubular ware in accordance with the invention can be undertaken incrementally, i.e., in a series of passes of the mandrel into the space defined by theroller means. Further, said roller. means may be adjusted to narrow the nip between the mandrel and themselves prior to each such pass therethrough. If necessary or desirable, the workpiece may be annealed, stress-relieved or the like between such passes.

Additionally, 'while the above description has been generally limited to the production of tapered wall tubular wares, it is obvious that the process and apparatus are also entirely suitable for the production of straight wall tubular wares by the simple expedient of employing a straight rather than tapered mandrel as explicitly shown and described.

Accordingly, it will be apparent than many different embodiments of this invention may be constructed; therefore, the above description and drawings are not intented to be limiting of the invention except .as is expressly indicated in the appended claims.

What is claimed is:

l. A process for producing cup-shaped metal wares having thin internally tapered walls, which process comprises: I

A. mounting a relatively thicker-walled cup-shaped metal workpiece in at least slip-fit relationship over the tip of a mandrel comprising a divergently tapered, continuous metalworking surface;

B. indirectly heating said workpiece by heating said mandrel;

C. providing at least one'heatedvroller means spaced from the divergently tapered, continuous metalsmaller dimension than the thickness of said thicker-walled workpiece is provided, the major portion of the heating of each said roller means being derived from a source other than said heated workpiece, and

D. causing relative motions of the resulting heated mandrel/heated workpiece assembly with respectto said heated roller means, motions comprisif xial motion of said assembly through said nip,

3. The process of claim 1 wherein said cup-shaped metal workpiece is mounted over the tip of said mandrel in press-fit relationship therewith.

. 4. The process of claim 1 wherein the workpiece comprises molybdenum, copper, nickel or tantalum.

5. The process of claim 1 wherein said workpiece comprises cross-rolled molybdenum and wherein said workpiece is heated to between about 375 F and about 425 F.

6. The process of claim 1 wherein the ware produced has a wall thickness at the thinnest point of less than about 0.01 inches.

7. The process of claim 1 wherein said roller means is maintained in a fixed position while the-heated mandrel/heated workpiece assembly is rotated and concurrently axially moved through said nip. I

8. The process of claim l wherein each of said roller means has at least one longitudinally stepped contour of increasing diameter. I

working surface of said mandrel whereby a nip of 

1. A process for producing cup-shaped metal wares having thin internally tapered walls, which process comprises: A. mounting a relatively thicker-walled cup-shaped metal workpiece in at least slip-fit relationship over the tip of a mandrel comprising a divergently tapered, continuouS metalworking surface; B. indirectly heating said workpiece by heating said mandrel; C. providing at least one heated roller means spaced from the divergently tapered, continuous metalworking surface of said mandrel whereby a nip of smaller dimension than the thickness of said thicker-walled workpiece is provided, the major portion of the heating of each said roller means being derived from a source other than said heated workpiece, and D. causing relative motions of the resulting heated mandrel/heated workpiece assembly with respect to said heated roller means, said motions comprising i. axial motion of said assembly through said nip, and ii. rotational motion between said assembly and said roller means.
 2. The process of claim 1 wherein at least two said heated roller means are positioned substantially equidistantly from and equiangularly about the circumference of the metalworking surface of the mandrel.
 3. The process of claim 1 wherein said cup-shaped metal workpiece is mounted over the tip of said mandrel in press-fit relationship therewith.
 4. The process of claim 1 wherein the workpiece comprises molybdenum, copper, nickel or tantalum.
 5. The process of claim 1 wherein said workpiece comprises cross-rolled molybdenum and wherein said workpiece is heated to between about 375* F and about 425* F.
 6. The process of claim 1 wherein the ware produced has a wall thickness at the thinnest point of less than about 0.01 inches.
 7. The process of claim 1 wherein said roller means is maintained in a fixed position while the heated mandrel/heated workpiece assembly is rotated and concurrently axially moved through said nip.
 8. The process of claim 1 wherein each of said roller means has at least one longitudinally stepped contour of increasing diameter. 